Digital measuring apparatus

ABSTRACT

A digital measuring apparatus for measuring the distance between two target lines formed on a test sample by the use of circular scanning or the like includes an optical pulse scale disposed in such a predetermined relationship with the target lines as to correct any measurement error resulting from circular (or angular) scanning. A scanning system is disposed to scan the target lines and the optical pulse scale in a predetermined relationship, thereby producing optical target-line position signals and optical pulse scale signals. Photoelectric converter means are provided to convert the optical target-line position signals and the optical pulse scale signals into respective electrical signals. Target-line position signal detector means may detect the target-line positions from one of the said electrical signals. The electrical signals passed through the target-line position signal detector means may be formed into gate signals by a gate circuit. The other electrical signals passed through the gate circuit are counted by counter means.

Elited gtates Patet [191 Nakazawa et a1.

[ DIGITAL MEASURING APPARATUS [75] Inventors: Kiwao Nakazawa,Sagamihara;

Shinya Sasayama, Tokyo, both of Japan [73] Assignee: Nippon Kogaku K.K.,Tokyo, Japan [22] Filed: May 18, 1972 [2]] Appl. No.1 254,469

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[111 3,791,735 [451' Feb. 12, 1974 Primary Examiner-Jt/laynard R. Wilbur[57 ABSTRACT A digital measuring apparatus for measuring the distancebetween two target lines formed on a test sample by the use of circularscanning or the like includes an optical pulse scale disposed in such apredetermined relationship with the target lines as to correct anymeasurement error resulting from circular (or angular) scanning. Ascanning system is disposed to scan the target lines and the opticalpulse scale in a predetermined relationship, thereby producing opticaltarget-line position signals and optical pulse scale signals.Photoelectric converter means are provided to convert the opticaltarget-line position signals and the optical pulse scale signals intorespective electrical sig nals. Target-line position signal detectormeans may detect the target-line positions from one of the saidelectrical signals. The electrical signals passed through thetarget-line position signal detector means may be formed into gatesignals by a gate circuit. The other electrical signals passed throughthe gate circuitare counted by counter means.

3 Claims, 8 Drawing Figures PM FEB?! SHEET 1 OF 2 Pammm 3791,73 5 sum a0? 2 6 PEG. 5 m. 6

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DIGITAL MEASURING APPARATUS BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to measuring apparatus, and moreparticularly to such apparatus in which a test sample, or the imagethereof, is optically scanned circularly (or angularly) for the purposeof photoelectrically and digitally measuring the positions of targetlines formed on the test sample, and the distance between and the amountof displacement of such target lines.

2. Description of the Prior Art Conventional apparatus of the describedtype measures the distance between the target lines on a test sample bythe use of a series of clock pulses having equal time intervalsjand suchuse of circular scanning has led to the measurement of the arcuatedistance, instead of the linear distance, between the target lines, thusresulting in a measurement error.

To correct such measurement error, the prior art has resorted to anapparatus which automatically varies the pulse intervals of the clockpulses in synchronism with the circular scanning, but such an apparatusis, of necessity, very complex.

SUMMARY OF THE INVENTION The present invention intends to correct themeasurement error resulting from circular scanning and to accomplishaccurate measurement of the target lines, without using theabove-described complex apparatus; but only by arranging an opticalpulse scale in a predetermined relationship with respect to a testsample and causing the test sample and the optical pulse scale to bescanned according to that predetermined relationship.

According to the present invention, there is provided an apparatus foroptically measuring the distance between two reference lines on a testsample. The apparatus comprises detector means revolvable to opticallyscan the reference lines on the test sample and thereby produce lightsignals representing the positions of the reference lines. A firstphotoelectric converter element is provided for converting the lightsignals into electrical signals.

The apparatus further comprises an optical pulse scale which includesalternately and equidistantly disposed parallel light transmittingportions and light intercepting portions, and pulse signal generatingmeans which is rotatable relative to the optical pulse scale opticallyto scan the same and thereby produce electrical pulse signals at leastfrom the time the detector means scans one of the reference lines untilit scans the other reference line.

The pulse signal generating means includes a first optical illuminatingsystem for illuminating therethrough the optical pulse scale with a finebeam of light, and a second photoelectric converter element forreceiving light from the first optical illuminating system through thelight transmitting portions and converting such light into electricalsignals.

The optical pulse scale is disposed so that the angles of the lighttransmitting and light intercepting portions thereof with respect to aline passing through the optical axis of the first optical illuminatingsystem to a point identical with the center of rotation of the pulsesignal generating means are equal to the angles of the reference lineswith respect to a line passing through the detector means to the centerof revolution of the detector means. The radius of revolution of thedetector means may be substantially equal to the radius of rotation ofthe pulse signal generating means relative to the optical pulse scale.

The apparatus further includes wave-form shaping means for shaping theelectrical signals into rectangular wave signals, an AND circuit havingtwo input terminals, one of which receives the rectangular wave signalsand the other of which receives the electrical pulse signals so that theelectrical pulse signals are gated by the rectangular wave signals toprovide, as output signals,

electrical pulse signals representing the portions corresponding to therectangular wave signals, and counter means for counting the electricalpulse signals passed 7 through the AND circuit.

The center of revolution of the detector means may be coincident withthe center of the pulse signal generating means; and the radius ofrevolution of the detector means may be equal to the radius of rotationof the pulse signal generating means.

The detector means may include a plate rotatably disposed in a planeidentical with a plane containing the reference lines, and a lighttransmitting member provided on the plate. The light transmitting memberhas an input end for sensing the reference lines to provide lightsignals and an output end for applying such light signals to the firstphotoelectric converter element adjacent thereto.

The optical pulse scale may be mounted on the rotatable plate and thefirst optical illuminating system is fixed at such a position that theoptical axis thereof passes within the circular locus of the opticalpulse scale, whereby at least from the time the light transmittingmember senses one of the reference lines until it senses the otherreference line, the first optical illuminating system scans the opticalpulse scale due to the relative revolution therebetween so that thesecond photoelectric converter element produces electrical pulsessignals.

The positionalrelationship of the reference line and the optical pulsescale with respect to the center of rotation of the rotary plate may beequal to the positional relationship between the input end of the lighttransmitting member and the optical axis of the first opticalilluminating system. The angles of the reference lines with respect to aline passing through the center of rotation of the rotatable plate tothe input end of the light transmitting member may be equal to theangles of the light transmitting and light intercepting portions of theoptical pulse scale with respect to a line passing through the center ofrotation to the optical axis of the first optical illuminating system.

There has thus been outlined rather broadly the more important featuresof the invention in order that the detailed description thereof thatfollows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described hereinafterand which will form the subject of the claims appended hereinto. Thoseskilled in the art will appreciate that the conception upon which thisdisclosure is based may readily be utilized as a basis for the designingof other structures for carrying out the several purposes of theinvention. It is important, there- 'fore, that the claims be regarded asincluding such equivalent construction as do not depart from the spiritand scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS A specific embodiment of the inventionhas been chosen for purposes of illustration and description, and isshown in the accompanying drawings, forming a part of the specification,wherein:

FIG. I is a diagram illustrating the manner in which the distancebetween two target lines is measured by circular scanning;

FIG. 2 is an illustration of the measuring method whereby themeasurement error arising in FIG. 1 is corrected in accordance with theprinciples of the present invention;

FIG. 3 is an enlarged view of an essential portion of FIG..2;

FIG. 4 is a combined schematic view and block diagram showing anembodiment of the present invention;

FIG. 5 illustrates a test sample; FIG. 6 illustrates the rotary discportion used in FIG.

FIG. 7 shows the waveforms of signals produced by circular scanning; and

FIG. 8 is a schematic representation of another embodiment of theapparatus according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principles of the presentinvention will first be described.

Referring to FIG. 1, it will be noted that target lines 1 and 2 areparallel to each other. For convenience of description, it is assumedthat both the target lines 1 and 2 make a bright, clear contrast withthe background. A straight center line X-X is parallel to the targetlines 1 and 2 passes through a center 0 which will later be described.

Numeral 3 designates the orbit followed by a point A as it is revolvedfor scanning along a circular line about the center point 0 so as tointersect the target lines 1 and 2. Actually, the point A may be amember formed with a pinhole-like opening and functioning to detectoptical signals representing the positions of the target lines 1 and 2,and such point A is hereinafter referred to as target-line positionsignal detecting sensor. If revolved for scanning along the scanningorbit 3, the target-line position signal detecting sensor A will scanthe target lines 1 and 2 at points P and P, whereupon there will beobtained optical signals representing the positions of the target lines1 and 2. When the distance [between the target lines 1 and 2 is to bemeasured, the optical signals of the target-line positions obtained inthe described manner may be converted into electrical signals and then,the number of clock pulses contained between these electrical signalsmay be counted by the use of a clock-pulse oscillator. However, suchclock pulses usually comprise a series of pulses having equal timeintervals, and, therefore, the measurement intended for the distancebetween the target lines 1 and 2 is actually the measurement of thelength of an arc PP because the point A follows a circular scanningorbit, thus failing to measure the true straight line distance 1 betweenthe target lines. This will be described more specifically with respectto FIG. 1, where the rad i us R of the circular scanning orbit isrepresented by GA, and the angles defined by the center lines X-X andthe points of intersection P, P between the targetline position signaldetecting sensor A and the target lines 1 and 2 are represented by 6 and0', respectively. The distance 1 between the target lines I and 2 may beexpressed as:

I R(Sin 0 +Sin 6) The sensor A is moved circularly at a uniform velocityalong the scanning orbit 3 between the points P and P, and it followsthat the measurement of the equal time intervals between the electricalposition signals at the points P and P effected by the use of theaforesaid clock pulses is actually the equal segmentation of the arc PPby such clock pulses, and after all, the length between the points P andP obtained by such easurement may be said to be the length of the arcPP.

Since the arc PP R(0 0' if the distance between the target lines 1 and 2is measured by the use of the circular scanning method and conventionalclock pulses, the result will suffer from the difference existingbetween equations (1) and (2) above. It will thus be obvious that suchan essential sine error occurring to the circular scanning system mustbe corrected.

FIG. 2 schematically illustrates a method of and an apparatus forcorrecting the above-described error in accordance with the principlesof the present invention.

Thus, in FIG. 2, an optical pulse scale 4 is disposed at a predeterminedlocation, as will now be described.

First, the location of the optical pulse scale 4 will be described withreference to FIG. 3 wherein the optical pulse scale 4 is formed withlight and dark lines 5 and 5 which occur at equal intervals. The opticalpulse scale 4 is so-positioned that these lines are parallel to thecenter line X-X crossing the circular scanning orbit 3. Since the centerlines XX is parallel to the target lines 1 and 2 as mentioned above, thelines 5, 5, formed on the optical pulse scale 4, are also parallel tothe target lines 1 and 2. When such a positional relationship isestablished for the target lines 1, 2 and the optical pulse scale 4 withrespect to the circular scanning orbit 3, it may be said that theoptical pulse scale 4 is out of phase with respect to the target lines1, 2.

Turning back to FIG. 2, a point designated at B has a pinhole-likeopening similar to that of the point A and functions to detect the lightand dark lines 5 and 5 formed on the optical pulse scale 4, and thepoint B may tentatively be referred to as optical pulse signal detectingsensor.

It is further assumed that the point B is at a position on the samecircular scanning orbit as followed by the target-line position signaldetecting sensor A but in a 180 out-of-phase relationship with thesensor A, that the optical pulse signal detecting sensor B comes to apoint Q on the optical pulse scale 4 when the target-line positionsignal detecting sensor A intersects the target line 1 at the point P,and that the optical pulse signal detecting sensor B comes to a point Qon the optical pulse scale 4 when the target-line position signaldetecting sensor A intersects the target line 2 at the point P.

In such a case, the target-line position signal detecting sensor A movescircularly to scan between the target lines 1 and 2 (or points P and P)while the optical pulse signal detecting sensor B is moving to scanbetween the points Q and Q on the optical pulse scale 4, so that thesensor A produces target-line position signals and the sensor B producespulse scale signals.

Also, assuming that the center line XX and the circular scanning orbit 3intersect each other at a point 13 on the optical pulse scale 4, it willbe seen that an optical pulse signal, produced as the optical pulsesignal detecting sensor B moves from the point Q to the point B alongthe circular scanning orbit 3 to scan the optical pulse scale 4 locatedat the said predetermined position, corresponds to a pulse signal formeasuring the sine variation occurring for the movement of the opticalpulse signal detecting sensor B on the circular scanning orbit 3,namely, for measuring an amount R Sin 0, where R (78. It will also beseen that a pulse scale signal produced as the optical pulse signaldetecting sensor B moves from the point B to the point Q along thecircular scanning orbit 3 to scan the optical pulse scale 4 correspondsto a pulse signal representing a length R Sin 6'.

Accordingly, the pulse scale signals, produced as the optical pulsesignal detecting sensor B scans from the point Q to the point Q,correspond to an amount R (Sin 0 Sin 0), which connotes the distance Ibetween the target lines 1 and 2 as is apparent from equation (1). Itwill thus be noted that the aforesaid sine error peculiar to thecircular scanning can be perfectly corrected by the present method Ithas been noted in respect of FIG. 2 that the optical pulse scale 4 andthe target lines 1 and 2 are disposed so as to be 180 out of phasewithrespect to the circular scanning orbit 3; and correspondingly, thetarget-line position signal detecing sensor A and the optical pulsesignal detecting sensor B are 180 out of phase wtih each other. However,depending on various cases, the phase relationship between the opticalscale 4 and the target lines 1, 2 and between the target-line positionsignal detecting sensor A and the optical pulse detecting sensor B, neednot always be 180. Rather, it is essential that the phase relationshipbetween the target lines 1, 2 and the optical pulse scale 4 be equal tothat between the target-line position signal detecting sensor A and theoptical pulse signal detecting sensor B, thereby enabling errorlessmeasurement to be accomplished by circular scanning.

Also, in FIG. 2, it has been assumed that the circular scanning orbit ofthe target-line position signal detecting sensor A and that of theoptical pulse signal detecting sensor B are identical with each other,whereas these two scanning orbits may be entirely different from eachother. In the latter case, however, it should be noted that thedistances over which the sensors A and B travel per unit of time aredifferent in accordance with the different radii of the scanning orbitsfollowed by the sensors A and B which, in turn, leads to the result thatthe length measure between the sensors A and B is not of the ratio ofl 1. Since such measure is equal to the ratiobetween the radii of thescanning orbits of the sensors A and B, as will be readily apparent,accurate measurement of the distance between the two target lines can beaccomplished by selecting the pitch of the lines formed on the opticalpulse scale 4 so as to compensate for the length measure.

Further, in FIG. 2, the target-line position signal detecting sensor Aand the optical pulse signal detecting sensor B have been shown ashaving a common center of scanning revolution, whereas they may havedistinct centers of revolution with their scanning revolutionsynchronized, thereby achieving the errorless measurement of thedistance between the target lines.

Furthermore, while FIG. 2 shows the two sensors A and B as beingcircularly movable for scanning, both sensors may be immovably fixed andthe target lines ll, 2 and the optical pulse scale 4 may be circularlymovable, resulting in the same measuring effect as described above.

Again in FIG. 2, the optical pulse signal detecting sensor B has beenshown as being circularly movable for scanning, but the same measuringeffect may be achieved by fixing this sensor B at the point B which isout .of phase with respect to the target lines 1, 2 disposing theoptical pulse scale 4 in 180 out-ofphase relationship with thetarget-line position signal detecting sensor A and moving this scale 4circularly for scanning.

Although the target lines have been assumed to take a bright, clearcontrast with the background, they need not always be linear, but may beof any suitable optical pattern representing the positions of boundaryportions between the light and the shade.

Accordingly, in the following description, the term target line isintended to be symbolic of an optical pattern for representing aposition. Further, the targetline position signal detecting sensor A andthe optical pulse signal detecting sensor B have both been assumed tohave a pinhole-like opening but, in fact, the opening may take any othershape in accordance with the pattern of the target lines or the opticalpulse scale. Furthermore, FIG. 2 has contemplated correction of theerror resulting from the target lines 1, 2 and the optical pulse scale 4being circularly scanned at the same velocity, whereas the sine error ofthe same nature may also occur in the measurement effected as by theordinary scanning mechanism utilizing the angular variation; andtherefore, the method as described hereinabove may equally be applicablefor such ordinary scanning mechanism.

It will thus be seen that the type of scanning is not limited tocircular scanning, but the ordinary scanning mechanism utilizing theangular variation may also be used.

The target lines 1, 2, optical pulse scale 4, target-line positionsignal detecting sensor A, optical pulse signal detecting sensor B,etc., which are arranged in such a relationship as to satisfy all thedescribed conditions, constitute a scanning system adapted to effectcircular scanning in the predetermined relationship as described above.

FIG. 4 shows a form of the present invention embodied in a digitaldisplacement measuring apparatus utilizing the above-described method oferrorlessly measuring the distance between two target lines through thecircular scanning system.

A test sample 6 to be measured, as shown in FIG. 5, has parallel targetlines 1 and 2 formed on the surface thereof at an interval (initialvalue), and it is assumed that the test sample 6 is such that, under acertain action, it is time-deformed in the direction of arrow 7 or 7'perpendicular to the target lines 1,2 until a certain point in time atwhich the target lines are displaced to the positions 1 and 2 to providea distance I therebetween.

The embodiment of FIG. 4 is intended to measure the distance between thetarget lines 1 and 2 at predetermined time intervals, thereby to obtainthe amount of displacement of such inter-line distance.

In FIG. 4, numeral 8 designates an optical imageforming system forforming the image of the sample 6 at a predetermined location and at apredetermined magnification.

A motor 9 drives to rotate a rotary disc 10 about a point 0 at apredetermined number of revolutions. As shown in FIG. 6, the rotary disc10 has attached thereto an optical fiber 11, as an optical guide, andthe input end A of the optical fiber 11 (which corresponds to thetarget-line position signal detecting sensor A in FIG. 2) can circularlymove along the orbit having a radius GA in accordance with the period ofrotation of the rotary disc 10 to scan the optical image 6 of the sample6 formed through the optical image'forming system 8, therebyperiodically detecting the positions of the target lines 1 and 2 on theformed sample image 6.

The rotary disc 10 carries thereon the optical pulse scale 4 which hasalready been described with respect to FIGS. 2 and 3. The light and darklines formed on the optical pulse scale 4 are disposed parallel to thestraight line GA, passing through the input end A of the optical fiber11 to the center of rotation O of the rotary disc 10 (and in 180out-of-phase relationship).

The point B as indicated on the optical pulse scale 4, lies on theextension from the straight line GA passing through the center 0, and aswill be later described, that is the point which is illuminated throughthe pinhole to read out optical pulse signals.

In FIG. 4, numeral 12 designates a photoelectric converter means bywhich the optical signals representing the positions of the target lines1 and 2 provided by the output end 11a of the optical fiber 11 may beconverted into electrical signals representing such positions.

When the target lines 1 and 2 are bright and clear with respect to thebackground, an electrical target-line position signal 23 produced by thephotoelectric converter means 12 will rise at the positions of thetarget lines 1 and 2, as indicated in FIG. 7(a), thus providing a pulsesignal having peaks 23a and 23b. Such electrical target-line positionsignal 23 is passed through amplifier means 13 to target-line positionsignal detector means 14, where the peak positions 23a and 23b of theelectrical signal 23 are electrically detected, and the detectionsignals of such peak positions are defined as target-line positionsignals.

The target-line position signals thus-obtained are used to form arectangular wave pulse signal 24 having rise and fall as shown in FIG.7(b), and a gate circuit uses the rectangular wave pulse signal 24 asgate signal for an electrical pulse scale signal 25, which will bedescribed below.

On the other hand, a pinholed plate 16 (FIG. 4), formed with a pinholeof predetermined dimensions, is

disposed for passing light from a light source 15 so that the pinholeimage may be formed at the point B through an optical image-formingsystem 17. As described previously, the point B is that at which theoptical pulse scale 4 (see FIG. 6) provided at a predetermined locationon the rotary disc 10 is illuminatedRotation of the rotary disc 10causes the optical pulse scale 4 to be rotated therewith, so that thepoint B moves relative to the optical pulse scale 4 to scan the lightand dark lines formed thereon. The optical pulse scale signalsrepresenting the light and the dark, thus produced, are applied tophotoelectric converter means 18, which converts the said optical pulsescale signals into an electrical pulse scale signal 25, as shown in FIG.7(c). In this regard, the measure of the image 6 of the test sample 6formed through the optical image-forming system 8 is the originalmeasure of the test sample multiplied by the magnification of suchoptical system 8. Also, if in FIG. 6 the radius 6A, of the circularorbit of the target-line position signal detecting sensor A is differentfrom the radius ($3 of the optical pulse scale read-out orbit, suchdifference will result in the measure OA/OB of the sample image 6' withrespect to the optical pulse scale 4, and therefore, the measure of thetest sample 6 with respect to the optical pulse scale 4 is, after all, ameasure resulting from such two factors. Thus, the pitch of the linesformed on the optical pulse scale 4 actually in use has been subjectedto such a correction.

The electrical pulse scale signal 25, which represents the true distancebetween the target lines as described previously, is passed throughamplifier means 19 to the gate circuit 20, where it is gated by theaforesaid gate signal or rectangular wave pulse signal 24 (FIG. 7(b),thereby providing an inter-target distance signal 26, as shown in FIG.7(d). The number of pulses contained in such inter-target distancesignal 26 may be counted by counter means 21 to thereby obtain the valueof the distance between the target lines.

Thus, when the sample object 6 is being timedeformed to vary the targetlines 1 and 2, the distance between the target lines may be digitallymeasured at predetermined time intervals without any error beinginvolved, and the speed of such measurement may be increased byshortening the period of scanning.

' Reverting again to FIG. 4, the displacement measurement may be fullyautomated by providing stop signal detector means 22 to detect a signalrepresenting either the stoppage of the deformation of the test sample 6or a predetermined limit of such deformation, and using the stop signalfrom the stop signal detector means 22 to stop the counter means 21.

FIG. 8 shows another embodiment of the present invention. Thisembodiment includes a laser oscillator 27, an optical system 28 forforming the laser light into a predetermined beam oflight, a mirror 29,and a beam splitter 30 through which light may be partly passed as lightbeam 31 and partly reflected as reflected beam 32.

A rotary reflection prism 34 is mounted at the center of rotation of arotary disc 10' connected to an electric motor 9' and is rotatable insynchronism' with the rotary disc 10'.

The reflected light beam 31 from the rotary reflection prism 34 scans atest sample 6" as the prism 34 is rotated. The surface of the sample 6is formed with target lines as in the embodiment of FIG. 5, and thesetarget lines are scanned by the light beam 31 to thereby produce opticaltarget-line position signals.

Thus, the light beam 31 is directed to scan the target lines and used asthe scanning beam for detecting the target-line positions.

Since the target lines may take various forms such as slits, points,boundaries between light and shade, etc., the pattern of the scanningbeam 31 on the test sample 6" should desirably be selected most suitablyin accordance with the variable form of the target lines in order toprovide target-line position signals of good S/N ratio. For thispurpose, an optical system 33 may be provided to form the most suitablepattern of the scanning beam.

As the light beam 31 scans the target lines on the test sample 6", thereare provided optical target-line position signals. Therefore, if thereflected light from the surface of the test sample 6" is condensed intothe photoelectric converter means 12' through an optical condensersystem 35, the photoelectric converter means 12 will produce electricalposition signals. On the other hand, the reflected light beam 32 fromthe beam splitter 30 passes via a mirror 36 and through an optical pulsescale illuminating system 37 to illuminate the optical pulse scale 4'disposed at a predetermined location on the rotary disc so that opticalpulse scale signals are produced with the rotation of the optical pulsescale 4' and converted into electrical pulse scale signals by thephotoelectric converter means 18.

The electrical target-line position signals and electrical pulse scalesignals produced in the described manner may be treated by the use of anelectrical treating system similar to that shown in FIG. 4, whereby thedistance between the target lines on the test sample 6" may be obtained.

The targetdine position signal detecting method using beam scanning asillustrated in FIG. 8 has the following features, as compared with thescanning method as illustrated in FIG. 4.

Firstly, the use of a laser as the source of the scanning beam leads toan effective utilization of the directivity, monochromatism and highbrightness of the laser beam which, in turn, leads to a good S/N rationof the resultant signals.

Secondly, any desired scanning method may be adopted relatively easilyfor the test sample.

Thirdly, the distance between the target lines may be long.

Fourthly, the optical image-forming system in use need not be of highperformance, and the adverse effect imparted to the measurement bymovement or tilting of the test sample may be relatively reduced.

Thus, according to the present invention, the measurement errorresulting from circular scanning can be perfectly corrected by a simplemechanical construction comprising a predetermined correlatedarrangement of the test sample 6, optical pulse scale 4, targetlineposition signal detecting sensor A, optical pulse signal detectingsensor B, etc., without the need to use any complex apparatus like theconventional one wherein the intervals between clock pulses aresynchronized with the circular scanning to provide automatic variations.

6 Moreover, when the test sample 6 to be measured has clear target lines1 and 2, errorless measurement is ensured irrespective of the type ofthe sample 6 and the displacement of the target lines may also bemeasuredreliably.

We believe that the construction and operation of our novel apparatuswill now be understood, and that its advantages will be fullyappreciated by those persons skilled in the art.

What is claimed is:

I. An apparatus for optically measuring the distance between twoparallel reference lines on an object comprising:

a focusing optical system for forming the image of said object,

a rotary plate which has an optical pulse scale including at itsperipheral portion parallel light transmitting portions and lightintercepting portions alternately and equidistantly disposed in thecircular di rection, and which is rotatable within the focusing plane ofsaid focusing system;

a driving means for rotating said rotary plate;

a photoconductive member fixed at its one end to the peripheral portionof said rotary plate so that the image of said object maybe scannedoptically by the rotation of said rotary plate and so that saidphotoconductive member may receive the optical signals of said referencelines;

a first photoelectric conversion means for converting the opticalsignals transmitted through said photoconductive member to electricalsignals;

a pulse signal generating means including a point optical source whichilluminates said optical pulse scale at least during the time intervalfrom a time when one of said two reference lines is scanned by saidphotoconductive member to a time when the other reference line isscanned, and a second photoelectric conversion means for converting theoptical pulse signals passing through said optical pulse scale toelectrical pulse signals;

a wave form shaping means for shaping said electrical pulse signals toprovide rectangular wave signals;

an AND circuit having two input terminals one of which receives saidrectangular wave signals and the other receives said electrical pulsesignals from said second photoelectric conversion means so that saidelectrical signals are gated by said rectangular wave signals toprovide, as output signals, electrical pulse signals corresponding tosaid rectangular wave signals; and

a counter means for counting the number of said electrical signalspassing through said AND circuit.

2. An apparatus for optically measuring the distance between twoparallel reference lines on an object comprising:

a laser source;

a rotary plate which has an optical pulse scale including at itsperipheral portion parallel light transmitting portions and lightintercepting portions disposed alternatively and equidistantly in thecircular direction, and which is rotatable;

a driving source for rotating said rotary plate;

a reflecting member fixed at the rotary center of said rotary plate forreflecting laser light from said laser source so that said object may bescanned by the rotation of said rotary plate;

a first photoelectric conversion means which receives the opticalsignals reflected by said object and converts said optical signals toelectrical signals;

a pulse generating means including a point light source whichilluminates said optical scale at least during the time interval from atime when one of said two reference lines is scanned by the rotationwhich receives said rectangular wave signals and the other receives saidelectric pulse signals from said second photoelectric conversion meansso that said electrical signals are gated by said rectangular of saidreflecting member to a time when the other wave signals to provide, asoutput signals, electric of said two reference lines is scanned, and asecond pulse signals corresponding to said rectangular photoelectricconversion means for converting to wave signals; and

electrical pulse signals light pulse signals generated a counter meansfor counting electric pulse signals from said point light source andpassed through passing through said AND circuit,

said optical pulse scale; 3. Apparatus according to claim 2, whereinsaid point a wave form shaping means for shaping the electrical lightsource is laser light divided by a beam splitter prosignals from saidfirst photoelectric conversion vided in the optical path of the laserlight generated means to provide rectangular wave signals; from saidlaser source.

an AND circuit having two input terminals one of v UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. ,7 5 D e February 12, 1974Inventor(s) KIWAO NAKAZAWA ET AL.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 2, line 41, change "pulses" to pulse line 62, change "hereinto"to hereto Column 4, line 2, change "line" to lines line 46, change"lines" to line Column 5, line 33, change (Sin 9 Sin 9') to (Sin 9 Sin9') line 42, change "detecing" to detecting line 43, change "wtih" towith Column 6, line 28, change "take" to make Column 10, linefl2, change"object," to object;

line 58, change 1"alter-natively" to alternately Column 11, line 2,after "optical", insert pulse Signed and sealed this 24th day ofSeptember 1974.

(SEAL) At testz v MCCOY M. GIBSON JR. 1 c. MARSHALL DANN AttestingOfficer 4 Commissioner of Patents FORM M050 (10-69) uscoMM-Dc 60376-P6QQ .5. GOVERNMENT PRINTHIG OFFICE I 569 36-33,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,791,735Dated February 12, 1974 Inventor(s) KIWAO NAKAZAWA ET AL.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 2, line 41, change "pulses" to pulse line 62, change "hereinto"to hereto Column 4, line 2, change "line" to lines line 46, change"lines" to line Column 5, line 33, change (Sin 9 Sin 9') to (Sin 9 Sin9') line 42, change "detecing" to detecting line 43, change "wtih" towith Column 6, line 28, change "take" to make Column 10, line 12, change"object," to object; line 58, change "alternatively" to alternatelyColumn 11, line 2, after "optical", insert pulse Signed and sealed this24th day of September 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. J c. MARSHALL DANN Attesting Officer Commissioner ofPatents USCOMM-DC 60376-P69 a uvs. GOVERNMENT PRINTING OFFICE: 19690-365-31.

F'ORN. J-105O (10-69)

1. An apparatus for optically measuring the distance between twoparallel reference lines on an object comprising: a focusing opticalsystem for forming the image of said object, a rotary plate which has anoptical pulse scale including at its peripheral portion parallel lighttransmitting portions and light intercepting portions alternately andequidistantly disposed in the circular direction, and which is rotatablewithin the focusing plane of said focusing system; a driving means forrotating said rotary plate; a photoconductive member fixed at its oneend to the peripheral portion of said rotary plate so that the image ofsaid object may be scanned optically by the rotation of said rotaryplate and so that said photoconductive member may receive the opticalsignals of said reference lines; a first photoelectric conversion meansfor converting the optical signals transmitted through saidphotoconductive member to electrical signals; a pulse signal generatingmeans including a point optical source which illuminates said opticalpulse scale at least during the time interval from a time when one ofsaid two reference lines is scanned by said photoconductive member to atime when the other reference line is scanned, and a secondphotoelectric conversion means for converting the optical pulse signalspassing through said optical pulse scale to electrical pulse signals; awave form shaping means for shaping said electrical pulse signals toprovide rectangular wave signals; an AND circuit having two inputterminals one of which receives said rectangular wave signals and theother receives said electrical pulse signals from said secondphotoelectric conversion means so that said electrical signals are gatedby said rectangular wave signals to provide, as output signals,electrical pulse signals corresponding to said rectangular wave signals;and a counter means for counting the number of said electrical signalspassing through said AND circuit.
 2. An apparatus for opticallymeasuring the distance between two parallel reference lines on an objectcomprising: a laser source; a rotary plate which has an optical pulsescale including at its peripheral portion parallel light transmittingportions and light intercepting portions disposed alternatively andequidistantly in the circular direction, and which is rotatable; adriving source for rotating said rotary plate; a reflecting member fixedat the rotary center of said rotary plate for reflecting laser lightfrom said laser source so that said object may be scanned by therotation of said rotary plate; a first photoelectric conversion meanswhich receives the optical signals reflected by said object and convertssaid optical signals to electrical signals; a pulse generating meansincluding a point light source which illuminates said optical scale atleast during the time interval from a time when one of said tworeference lines is scanned by the rotation of said reflecting member toa time when the other of said two reference lines is scanned, and asecond photoelectric conversion means for converting to electrical pulsesignals light pulse signals generated from said point light source andpassed through said optical pulse scale; a wave form shaping means forshaping the electrical signAls from said first photoelectric conversionmeans to provide rectangular wave signals; an AND circuit having twoinput terminals one of which receives said rectangular wave signals andthe other receives said electric pulse signals from said secondphotoelectric conversion means so that said electrical signals are gatedby said rectangular wave signals to provide, as output signals, electricpulse signals corresponding to said rectangular wave signals; and acounter means for counting electric pulse signals passing through saidAND circuit.
 3. Apparatus according to claim 2, wherein said point lightsource is laser light divided by a beam splitter provided in the opticalpath of the laser light generated from said laser source.